Some adventurous types like to investigate the hidden or (frequently) off-limits areas of infrastructure in and around Davis. These places include utility tunnels, rooftops, abandoned buildings, and sewers. While, technically speaking, this activity often involves trespassing, ethical urban explorers are most often like old-school hackers in that they intend to do no damage and only learn more about interesting places. This isn't to say that it's not dangerous. For more information in this pursuit in general, see the article on Wikepedia.